This invention relates to the field of water filtration and in particular to a particle precipitator intended for use alone or in combination with other filters including sand and screen filters.
Fluid filtration including particle separation is desirable for a wide variety of purposes. For example, where irrigation water is scarce, particularly in more arid areas, a farmer is likely to look to almost any source of raw water, no matter how dirty to keep his fields irrigated and crops prosperous. It is axiomatic however, that any particles in the farmer's irrigation water can cause severe problems. These problems include clogging of the conduits and spraying devices as well as the eventual undesirable filling in of naturally aerated soil with fine particles that can ruin the productivity of the soil. Other uses for filtration systems include sewage treatment and water purification.
Over the years, a large number of fluid filtration systems have been developed to meet the wide variety of needs alluded to above. One well known filter especially useful for the filtration of raw water to be used for irrigation is a media filter. Although media filters come in all shapes and sizes, a good example of a basic media filter comprises an upstanding cylindrical tank having an opening in the top for accepting raw water and a discharge port at the bottom for discharging filtered water. The port at the bottom of the tank generally will have a collector screen to prevent the filter media from escaping. The filter media itself can be a variety of materials but normally will be a layer of gravel at the bottom covered by a layer of finer sand which will fill most of the cylindrical tank.
Another type of filter that is in common use is a screen filter. Screen filters generally will consist of a cylindrical tank with a concentric cylindrical screen inside the tank and extending along the length thereof. Raw water is pumped into the middle of the screen and exits the tank from the outside portion of the screen.
As particles clog the pores of the screen and media filters, these filters become less efficient and eventually the flow rate becomes untolerably low. At this point these filters must be back washed to get rid of the silt and particles that have clogged up the filter pores. It is obvious that the longer the period that a filter lasts between back washes, the better. As both the screen and the media filters are designed to filter out fairly fine particles it can be seen that if the raw water being filtered has a large number of reasonably large sized particles, these filters will become clogged quickly and will require back washing at very short intervals. One solution to this problem is to provide some sort of separator to remove the larger particles before they reach the screen or media filter.
In the case of the media filter, the applicant is aware of at least one firm that provides a particle separator to accept the raw water before it reaches the media filter. The separator is a dumb-bell shaped container which is mounted at an angle to the ground of about 40.degree. to 47.degree.. Raw water is introduced at the upper dumb-bell portion tangentially to the interior surface of the container and at a high velocity. This causes the water within the container to rotate at a fairly high speed forcing heavier particles to the surface of the container and eventually to the bottom portion thereof. A pipe is placed in the center of the whirling water about half or three-quarters of the way down through the container from the top. This pipe siphons off the cleaner water from the middle and directs it to the next stage filter which can, for example, be a media filter. Some of the drawbacks of this system are that it takes up a substantial amount of space and it requires a high velocity and thus high pressure operation which is expensive to provide.
Another particle separator known to the applicant comprises a rectangular elongated closed box which has baffles along the bottom and/or top surface. Water flows from one side of the box to the other side of the box through the path created by the baffles. The baffles act to slow down the flow and thus permit particles to separate out and fall to the bottom of the box.
Another separator known to the applicant involves an elongated rectangular box having no baffles in it and tilted at an angle of about 47.degree.. The water enters the box at the lower end thereof and is in theory designed to flow at a rate such that the fluid flow is laminar from the bottom to the exit at the top of the box. During the period that the fluid is within the box, particles precipitate out and fall eventually to the bottom portion of the box.
A sedimentation tank similar to the one discussed above in connection with the baffles in the rectangular box is shown in a U.S. patent issued to D. E. Bradford on July 20, 1965 having U.S. Pat. No. 3,196,141 and entitled "Recovery of Solids From a Liquid-Solid Slurry". The chemical slurry is introduced at one end of a tank 2 which contains a series of internal baffles 18. The baffles aid sedimentation by slowing down the flow of the fluid. Such tanks are fairly expensive to build and have substantial space requirements.
The U.S. patent issued to K. Seidel on Nov. 6, 1973, having U.S. Pat. No. 3,770,623, and entitled "System for Purification of Polluted Water" shows a combination of a settling tank 11 and a series of filtration beds 13. The settling tank is square and has a series of internal baffles 20 to slow down the flow of water. The settling tank is intended to collect the most coarse sediment 10 (see FIG. 4) before the fluid flows into the filtration beds. The invention is directed to incorporating plants in the filtration process to obtain a better purification effect. It is clear that the disclosed filtration system is rather bulky and requires a large commitment in space as well as a substantial amount of maintenance to make the system operate properly.
A United States patent issued to Krone on Dec. 11, 1979, having U.S. Pat. No. 4,178,252 and entitled "Device for Separating Particles From a Fluid Suspension and Method For Doing So" shows a cylindrical sedimentation tank in FIGS. 2 and 3. Raw water is introduced into the tank by tubes 48 and 49 which extend into the annular space between the wall 42 of the cylindrical tank and the inner concentric cylindrical baffle 45. The water goes up through the annular space between the baffle 45 and the wall of the tank 42 out into the main part of the tank and then down through weir 52 into pipe 53. The heavy particles are intended to precipitate to the bottom and light ones to rise to the top of the surface of the water between the point when the water leaves the top of the annular space between baffle 45 and wall 42 and time when it reaches weir 52. The theory of the patent is that by providing a rotating cylindrical wall in the annular space between baffle 45 and wall 42, shear forces will be created which will act to help somehow in separating particles from the water. Because the raw water emerges from the narrow annular space created between baffle 45 and wall 42 at a level close to that of the weir 52, the flow rates involved would necessarily have to be extremely slow in order to provide sufficient time for particles to either float to the top or precipitate to the bottom before reaching weir 52. Furthermore, the annular baffle 45 and moving, cylindrical, shear creating wall 56 will be somewhat expensive to manufacture and maintain.
The U.S. patent issued to Moll et al., on Oct. 27, 1981, U.S. Pat. No. 4,297,221, and entitled "Process and Apparatus for the Treatment of Untreated Water" discloses a cylindrical sedimentation tank with an annular perforated baffle spaced concentrically inward from the outer wall of the tank. Water, treated with some kind of flocculating agent, is introduced tangentially into the cylindrical tank through port 5. The circular flow of the water is slowed down by the annular baffle so that the flocculating agent has time to collect particles together so that they precipitate to the bottom of the tank. The cleaner water is drawn off from the top of the tank through centrally located pipe 7. Although this device works fine for turbid water into which flocculating agents have been inserted, larger particles may clog up the perforated baffle 3. In addition, circumferential baffles of this nature are somewhat difficult to construct and therefore make the end product fairly expensive.